Battery separator with improved oxidation stability

ABSTRACT

The invention relates to a thermoplastic polymer-based battery separator, which contains a compound of formula R(OR 1 ) n  (COOM x+   1/x ) m . In said formula, R represents a non-aromatic hydrocarbon group comprising between 10 and 4,200 carbon atoms, which can be interrupted by oxygen atoms, R 1  represents H, —(CH 2 ) k COOM x+   1/x  or —(CH 2 ) k —SO 3 M x+   1/x , whereby k stands for 1 or 2, M represents an alkali or earth alkaline metal ion, H +  or NH 4   + , whereby not all variables of M are defined simultaneously as H + , n stands for 0 or 1, m stands for 0 or a whole number from 10 to 1,400 and x stands for 1 or 2. The ratio of oxygen atoms to carbon atoms in the compound according to the aforementioned formula ranges between 1:1.5 and 1:30 and n and m cannot simultaneously represent zero.

The invention relates to separators for lead/sulphuric acidaccumulators, hereafter called lead accumulator for short, which have animproved oxidation resistance.

The separators used today in lead accumulators are mostly filled,microporous polyolefin separators. These are intended on the one hand toprevent a direct contact and thus short circuits between the electrodeplates, and on the other hand to make possible an ionic current flow andoffer this the smallest possible resistance. The composition andproduction of such separators are known per se (cf. e.g. DE-PS 1 267423, DE-PS 1 298 712, DE-AS 1 496 123, DE-OS 35 45 615, DE-PS 35 40 718and DE-PS 36 17 318).

According to U.S. Pat. No. 3,351,495, to this end a homogeneous mixtureof polyolefin, filler, plasticizer and additives is formed and this isformed into a web-shaped layer. Then the plasticizer and fillers are atleast partly removed by extraction. Polyethylene glycol, glycerin and inparticular mineral oil are used as plasticizer. To prevent an oxidativedegradation of the polyolefin during extrusion the separators can alsocontain antioxidants such as 4,4-thio-bis-(6-tert-butyl-m-cresol) and2,6-di-tert-butyl-4-methylphenol.

When in use the separators must not only resist the aggressive batteryacid but are also exposed, particularly in the area of the positiveplate, to oxidative attacks, for example by oxidative lead dioxide andthe formation of extremely reactive nascent oxygen and peroxides. Inaddition to this, lead accumulators are exposed to ever higher ambienttemperatures and cycle loads, which further intensifies the oxidativeattack.

Although the polyethylene frequently used for the production of theseparators does give the separators, in combination with smallquantities of antioxidant and a larger quantity of oil, a certainoxidation stability vis-à-vis the aggressive medium of the battery, theseparator material can still undergo slow oxidative attack under moredifficult conditions of use and finally be destroyed, which results in adeterioration of the mechanical stability of the separator and theformation of cracks and holes and which in the most unfavourable caseshortens the battery life through short circuits.

Many measures for improving the oxidation stability of batteryseparators are known. For example, the oxidative degradation of theseparator can be delayed by increasing the separator thickness, themolecular weight of the polymer used to produce the separator or througha significant increase in the polymer content of the separator.

However, an increase in the separator thickness leads to appreciablyhigher production costs and higher electrical resistances. Theultra-high molecular-weight polyethylene (UHMWPE) customarily used toproduce separators also generally already has a molecular weight of5−7×10⁶ g/mol and a further increase in the molecular weight would leadto considerable process problems. Moreover, although UHMWPE types with amolecular weight of up to approximately 10×10⁶ g/mol are commerciallyavailable, the polymer chains of these UHMWPE types are markedlydegraded during extrusion by shearing in the extruder, which againsubstantially reduces the molecular weight. An increase in the polymercontent causes the wettability and porosity and thus the electricalresistance of the separator to deteriorate significantly.

It is also known from the state of the art that the process oils used toproduce the battery separators can improve the oxidation resistance ofthe separators The maximum oil content of the separators is restrictedhowever, because the oil also causes the wettability and porosity of theseparator to deteriorate.

DE 30 04 659 C2 discloses separators which contain oils with anaromatics content of at least 40%. Because of their composition, theseoils bring about an improvement in the oxidation resistance of theseparators. However, process oils with a high aromatics content canencourage the formation of dark, often sticky deposits in the leadaccumulator which contaminate the inside and outside of the accumulatorcase and can block the valve systems.

The prevention of such deposits is the subject-matter of DE 39 22 160A1, which to this end discloses the use of surfactants, preferably ofthe amide or amine type.

JP 02155161 A discloses the use of a combination of paraffin oil,antioxidant and a peroxide decomposer based on phosphoric acid toimprove the oxidation stability of battery separators at hightemperatures. However this does not provide protection against theoxidative effect of nascent oxygen or of the lead dioxide of thepositive electrode plate.

JP 07130348 A discloses separators which contain mineral oil incombination with a phenolic resin.

To improve the oxidation stability of pocket separators an increase inthe oil content in the fold edge and along the weld edge is proposed inU.S. Pat. No. 5,384,211 and JP 10031992 A.

JP 08203493 A discloses the coating of the edges of separators with aninsulating resin in order to suppress the oxidative attack.

JP 2000133239 A describes the coating of the upper part of theseparator, which is in contact with the frame and the electrode lug ofthe positive plate, with a hot-melt adhesive.

The above separators cannot be produced continuously with today'stechniques, and the process is thus time-consuming and expensive.Moreover only a partial improvement in oxidation stability is achieved.

It is customary to provide separators with longitudinal ribs on at leastone side in order to prevent direct contact of the separator sheet withthe positive electrode plate and thus a premature oxidative destruction.

JP 04167356 A and JP 2000182593 A disclose separators which haveadditional ribs in the area of the weld edges of the separators in orderto prevent in a targeted way the formation of cracks through oxidationin this area.

JP 09097601 A discloses separators profiled, in a particular way whichallow the gas which forms on the positive plate to escape more quicklyand are thus, intended to reduce its oxidative effect on the separator.

JP 04190554 A describes the addition of glass fibres to the separatormaterial in order to delay a deterioration of the mechanical propertiesof the separator through oxidation. The introduction of glass fibresinto the separator by extrusion is difficult however, because glassfibres on the one hand are dispersible only with difficulty in theseparator material and on the other hand break easily during extrusionand block the extruder screens. Also, separators containing glass fibresare not very flexible and tend to break when subjected to a mechanicalstress.

Despite considerable efforts, none of the present methods for improvingthe oxidation resistance of battery separators is completelysatisfactory.

Battery separators are known from U.S. Pat. No. 4,024,323 in which atleast 40% of the ultra-high molecular-weight polyethylene used for theproduction of separators are replaced by a copolymer of an olefin and(meth)acrylic acid or a mixture of a polyolefin of low molecular weightand a polymer of (meth)acrylic acid. This is intended to increase theextrusion speed and improve the incorporation of the filler into thepolymer. The replacement of at least 40% of the ultra-highmolecular-weight polyethylene by low-molecular-weight polymers isdisadvantageous, however, because it leads to a deterioration of themechanical properties of the separator.

The object of the invention is to provide battery separators with highoxidation stability which are easy and inexpensive to produce and whichare protected over their whole surface against oxidation.

According to the invention this object is achieved by battery separatorswhich contain a compound with the Formula (I)R(OR¹)_(n)(COOM^(x+) _(1/x))_(m)  (I)in which

-   R is a non-aromatic hydrocarbon radical with 10 to 4200 carbon    atoms, preferably 13 to 4200, which can be interrupted by oxygen    atoms,-   R¹ is H, —(CH₂)_(k)COOM^(x+) _(1/x) or —(CH₂)_(k)—SO₃M^(X+) _(1/X),    preferably H, where k is 1 or 2,-   M is an alkali metal or alkaline-earth metal ion, H⁺ or NH₄ ⁺, where    not all the variables M simultaneously have the meaning H⁺,-   n is 0 or 1,-   m is 0 or an integer from 10 to 1400 and-   x is 1 or 2,    the ratio of oxygen atoms to carbon atoms in the compound according    to Formula (I) being in the range from 1:1.5 to 1:30 and m and n not    being able to simultaneously be 0. However, preferably only one of    the variables n and m is different from 0.

By non-aromatic hydrocarbon radicals is meant radicals which contain noaromatic groups or which themselves represent one. The hydrocarbonradicals can be interrupted by oxygen atoms, i.e. contain one or moreether groups.

R is preferably a straight-chain or branched aliphatic hydrocarbonradical which can be interrupted by oxygen atoms. Saturated,uncross-linked hydrocarbon radicals are quite particularly preferred.

Surprisingly it was found that through the use of the compounds ofFormula (I) for the production of battery separators, they can beeffectively protected against oxidative destruction.

Battery separators are preferred which contain a compound according toFormula (I) in which

-   R is a hydrocarbon radical with 10 to 180, preferably 12 to 75 and    quite particularly preferably 14 to 40 carbon atoms, which can be    interrupted by 1 to 60, preferably 1 to 20 and quite particularly    preferably 1 to 8 oxygen atoms, particularly preferably a    hydrocarbon radical of formula R²—[(OC₂H₄)_(p)(OC₃H₆)_(q)]—, in    which    -   R² is an alkyl radical with 10 to 30 carbon atoms, preferably 12        to 25, particularly preferably 14 to 20 carbon atoms,    -   p is an integer from 0 to 30, preferably 0 to 10, particularly        preferably 0 to 4 and    -   q is an integer from 0 to 30, preferably 0 to 10, particularly        preferably 0 to 4,    -   compounds being particularly preferred in which the sum of p and        q is 0 to 10, in particular 0 to 4,-   n is 1 and-   m is 0.

Formula R²—[(OC₂H₄)_(p)(OC₃H₆)_(q)]— is to be understood as alsoincluding those compounds in which the sequence of the groups in squarebrackets differs from that shown. For example according to the inventioncompounds are suitable in which the radical in brackets is formed byalternating (OC₂H₄) and (OC₃H₆) groups.

Additives in which R² is a straight-chain or branched alkyl radical with10 to 20, preferably 14 to 18 carbon atoms have proved to beparticularly advantageous. OC₂H₄ preferably stands for OCH₂CH₂, OC₃H₆for OCH(CH₃)CH₂ and/or OCH₂CH(CH₃)

As preferred additives there may be mentioned in particular alcohols(p=q=0; m=0) primary alcohols being particularly preferred, fattyalcohol ethoxylates (p=1 to 4, q=0), fatty alcohol propoxylates (p=0;q=1 to 4) and fatty alcohol alkoxylates (p=1 to 2; q=1 to 4) ethoxylatesof primary alcohols being preferred. The fatty alcohol alkoxylates arefor example accessible through reaction of the corresponding alcoholswith ethylene oxide or propylene oxide.

Additives of the type m=0 which are not, or only difficultly, soluble inwater and sulphuric acid have proved to be particularly advantageous.

Also preferred are battery separators which contain a compound accordingto Formula (I), in which

-   R is an alkane radical with 20 to 4200, preferably 50 to 750 and    quite particularly preferably 80 to 225 carbon atoms,-   M is an alkali metal or alkaline-earth metal ion, H⁺ or NH₄ ⁺, in    particular an alkali metal ion such as Li⁺, Na⁺ and K⁺ or H⁺, where    not all the variables M simultaneously have the meaning H⁺,-   n is 0,-   m is an integer from 10 to 1400 and-   x is 1 or 2.

As suitable additives there may be mentioned here in particularpolyacrylic acids, polymethacrylic acids and acrylic acid-methacrylicacid copolymers, whose acid groups are at least partly, i.e. preferably40%, particularly preferably 80 %, neutralized. The percentage refers tothe number of acid groups. Quite particularly preferred arepoly(meth)acrylic acids which are present entirely in the salt form. Bypoly(meth)acrylic acids are meant polyacrylic acids, polymethacrylicacids and acrylic acid-methacrylic acid copolymers. Poly(meth)acrylicacids are preferred and in particular polyacrylic acids with an averagemolar mass M_(w) of 1,000 to 100,000 g/mol, particularly preferably1,000 to 15,000 g/mol and quite particularly preferably 1,000 to 4,000g/mol. The molecular weight of the poly(meth)acrylic acid polymers andcopolymers is ascertained by measuring the viscosity of a 1% aqueoussolution, neutralized with sodium hydroxide solution, of the polymer(Fikentscher's constant).

Also suitable are copolymers of (meth)acrylic acid, in particularcopolymers which, besides (meth)acrylic acid contain ethylene, maleicacid, methyl acrylate, ethyl acrylate, butyl acrylate and/or ethylhexylacrylate as comonomer. Copolymers are preferred which contain at least40 wt.-%, preferably at least 80 wt.-% (meth)acrylic acid monomer, thepercentages being based on the acid form of the monomers or polymers.

To neutralize the polyacrylic acid polymers and copolymers, alkali metaland alkaline-earth metal hydroxides such as potassium hydroxide and inparticular sodium hydroxide are particularly suitable.

Suitable additives according to the invention are known and arecommercially available.

As well as the named additives the separators can alternatively oradditionally contain compounds which can form the additives according tothe invention. Preferred are compounds which, when the separators areused for the intended purpose release suitable additives, for example byhydrolysis with the battery acid. Particularly suitable substances ofthis type are esters which form, OH-group-containing compounds ofFormula (I). These include for example phthalic acid esters of theabove-named alcohols.

The battery separators can be provided in various ways with the additiveor additives. The additives can for example be applied to the separatorwhen it is finished (i.e. after the extraction) or added to the mixture,used to produce the separator. According to a preferred embodiment theadditive or a solution of the additive is applied to the surface of theseparator. This variant is suitable in particular for the application ofnon-thermostable additives and additives which are soluble in thesolvent used for the subsequent extractions. Particularly suitable assolvents for the additives according to the invention arelow-molecular-weight alcohols, such as methanol and ethanol, as well asmixtures of these alcohols with water. The application can take place onthe side facing the negative electrode, the side facing the positiveelectrode or on both sides of the separator. In the case of anapplication on one side, an application to the side of the separatorfacing the positive electrode plate is preferred.

The application may also take place by dipping the battery separator inthe additive or a solution of the additive and subsequently optionallyremoving the solvent, e.g. by drying. In this way the application of theadditive can be combined for example, with the extraction often appliedduring separator production.

Another preferred option is to mix the additive or additives into themixture of thermoplastic polymer and optionally fillers and otheradditives which is used to produce the battery separators. Theadditive-containing homogeneous mixture is then formed into a web-shapedmaterial. Because this usually occurs by extrusion at high temperature,difficultly volatile and thermostable additives which are difficultlysoluble in the solvent used for extraction, such as polyacrylic acidpolymers and copolymers or their salts, are particularly suitable forthis.

The additives can be used alone or as a mixture of two or, moreadditives. Mixtures of one or more of the additives according to theinvention with surfactants, defoamers and other additives can also beused.

The additives used according to the invention are preferably used in aquantity of 0.5 to 50 wt.-% particularly preferably 1.0 to 5.0 wt.-%,quite particularly preferably 1.5 to 4.0 wt.-% and in particular 2.0 to3.5 wt.-% relative to the mass of the separator after the extraction.

The additives used to produce the separators preferably have a highboiling point. Additives with a boiling point of 250° C. or more haveproved to be particularly suitable.

The additives used according to the invention are suitable for combiningwith all separators which are liable to oxidative attacks, in particularfor combining with separators based on thermoplastics. Separators which,as well as a thermoplastic, also contain a filler and oil are quiteparticularly preferred.

Preferably the additives are combined with separators based onpolyolefins, particularly preferably filler-containing polyolefins whichcan be produced by hot-forming such as extrusion or pressing, andsubsequent extraction. The additives are however also suitable for theprotection of separators which contain polyolefin threads or fibres,e.g. separators in the form of fleeces.

Preferred polyolefins are polyethylenes, ultra-high molecular-weightpolyethylene being particularly preferred according to the invention.Ultra-high molecular-weight polyolefin with an average molecular weightby weight of at least 300,000, preferably at least 1.0×10⁶ andparticularly preferably at least 5.0×10⁶ g/mol is quite particularlypreferred.

The molecular weight of the polyethylene is measured by the Margoliesequation: M=5.37×10⁴[η]^(1.49); with η=reduced specific viscosity indl/g (Josef Berzen, CZ Chemie-Technik, 3^(rd) Volume (1974) No. 4, p.129).

However polypropylene, polybutene, polystyrene, ethylene-propylenecopolymers, ethylene-hexylene copolymers, ethylene-butene copolymers,propylene-butene copolymers and ethylene-propylene-butene copolymers arealso suitable.

The separators according to the invention preferably contain 10 to 100wt.-%, particularly preferably 15 to 50 wt.-% and quite particularlypreferably 20 to 40 wt.-% polymer, in particular ultra-highmolecular-weight polyethylene, relative to the sum of the weights offiller and polymer.

A filler preferred according to the invention is SiO₂, quiteparticularly preferred fillers are amorphous precipitation silicas.Oxides and hydroxides of silicon, aluminium and titanium as well asmica, talc, silicates and glass beads are also suitable as fillers.Fillers of this type are disclosed for example in U.S. Pat. No.3,351,495 and DE 14 96 123 A.

The separators according to the invention preferably contain 0 to 90wt.-%, particularly preferably 50 to 85 wt.-% and quite particularlypreferably 60 to 80 wt.-% filler, relative to the sum of the weights offiller and polymer, silicas preferably being exclusively used as filler.

The weight ratio of filler to polymer is preferably 0 to 9.0,particularly preferably 1.0 to 5.7 and quite particularly preferably 1.5to 4.0.

Extractable oils which tact on the one hand as plasticizers and on theother hand as pore-formers are in particular used as further additives.The liquids disclosed in DE 12 67 423 A, such as for example processoils, are particularly suited. By oils or process oils are preferablymeant mineral oils. The oil content in the separator is preferably 5 to35 wt.-%, particularly preferably 8 to 30 wt.-%, and quite particularlypreferably 10 to 25 wt.-% relative to the total mass of the separatorafter the extraction.

Apart from the main constituents named above, the separators can containother customary constituents such as carbon black, antioxidants such asfor example alkylidene-bisphenols, lubricants, other fillers such as forexample talc etc., and optionally also other polymers in more or lesssecondary quantities. Carbon black is preferably used in a quantity ofat most 5 wt.-%, the other additives preferably in a quantity of at most2 wt.-%, relative in each case to the total mass of the finishedseparator.

To produce the separators the named materials are carefully mixed in theusual way and then formed into a web-shaped material accompanied byheating. The oil is then extracted from this for example with an organicsolvent such as hexane so that the desired porosity is obtained. Finallythe separator material is cut to size according to the desired usageform, i.e. preferably cut to the final width, wound up into rollsapproximately 1,000 metres in length and packed. The surfaces of theseparator can be smooth, ribbed or shaped in any other way. Thecomposition and production of battery separators is sufficiently knownfrom the above-mentioned state of the art. In so far as the additivesused according to the invention are soluble in the extraction agent orare able to be extracted with it, they are applied to the separatorpreferably after the extraction step. The additives can however also beadded to the extracting agent and thus be applied to the separatorduring the extraction.

The separators are mostly used in the form of pockets into which thepositive or negative electrode plates are inserted. The pocketedelectrode plates are then joined, to oppositely-charged non-pocketedelectrode plates to form blocks of plates and inserted into a batterycontainer. After filling with sulphuric acid and sealing with a batteryblock cover the lead accumulator is complete.

The subject-matter of the invention are also lead-sulphuric acidaccumulators with at least two oppositely-charged electrode plates whichcontain at least one, battery separator with one of the additivesaccording to the invention.

Apart from the additives used according to the invention theaccumulators are customary lead/sulphuric acid accumulators withconventional electrodes and sulphuric acid as electrolyte. Preferablythey are starter batteries for motor vehicles. The case can be made ofall the customary materials, e.g. polypropylene, hard rubber, acrylicglass, polystyrene, glass etc.

The invention is explained in more detail in the following withreference to embodiments.

EXAMPLES Examples 1-7

Use of 1-Dodecanol as Additive to Prevent Premature Oxidation of BatterySeparators

Unless stated otherwise battery separators based on polyethylene(UHMWPE) and precipitation silicic acid, are used in the examples. Theseparators are produced on an extruder according to U.S. Pat. No.3,351,495 and after extrusion are extracted with hexane to an oilcontent in the base sheet of approximately 12 wt.-% The weight ratio offiller to polymer that is used is given in the respective examples.

In order to assess the effectiveness of the additives a standardizedoxidation test was used (PEROX 80 Test) which largely corresponds to themethod recommended by the BCI (Battery Council International) fordetermining the oxidation stability of battery separators(TM-3.229:Standard test method to determine resistance of battery separator tooxidative degradation using hydrogen peroxide in sulphuric acid asoxidizing medium).

To this end, testpieces from the separator material were treated with amixture of sulphuric acid and hydrogen peroxide at 80° C. for varioustime periods and the extension of the material before and after the testwas compared. The reduction in extendability is a measure of thedegradation and the cross-linking, i.e. the oxidative destruction of thepolymer. Separators without additives according to the invention whichwere tested under identical conditions served as comparison.

The testpieces were bone-shaped in accordance with DIN 53455. Theoxidation solution was always freshly prepared, and consisted of 360 mlsulphuric acid of density 1.28 g/cm³, 35 ml sulphuric acid of density1.84 g/cm³ and 105 ml 35% hydrogen peroxide solution. The componentswere slowly mixed with each other accompanied by stirring in the givenorder and then heated to 80° C. in a closed glass vessel in a waterbath. Two sample holders each with five testpieces were placed insolution and left in the solution for the desired test period. Then, thesamples were washed acid free with lukewarm water and the extension wasmeasured. To this end the testpieces were stretched to breaking at atest speed of 300 mm/min. The extension in cross machine direction (CMD)(CMD-expansion) was measured. In each of the following tables theaverage of ten measured values is given. Because the initial extensionof the separators can vary for process reasons, the absolute expansionswere normalized to the initial expansion:absolute stretching after x h Perox Test in %/absolute stretching after0 h Perox Test in %×100=relative expansion after x h Perox Test

In examples 2 to 7 separator sheets 160×300 mm in size were coated onone side with an ethanol solution of 1-dodecanol so that after dryingthere was 0.7 to 7.1 wt.-% 1-dodecanol on the blade. In the examples,unless stated otherwise, all weight percentages refer to the weight ofthe separator after extraction. An untreated separator served ascomparison (Example 1). In examples 1 to 7 the weight ratio of filler topolymer was 2.6 in each case.

The separators coated with the additive were subjected to the oxidationtest described above. After the test had ended the separators coatedwith 1-dodecanol showed a considerably higher residual expansion thanthe untreated separator (see Table 1). The results compiled in Table 1prove that 1-dodecanol, even in extreme test conditions (80° C., H₂O₂)and in small concentrations guarantees improved protection of theseparator vis-à-vis oxidative destruction. TABLE 1 Oxidation resistanceof separators after treatment with 1-dodecanol (oxidation test) Example1*) 2 3 4 5 6 7 Quantity of 0 0.7 1.4 2.1 2.8 3.5 7.1 additive [wt.- %]Duration of the oxidation test Absolute extension [%]  0 h 263 269 282266 271 267 291 20 h 152 186 234 235 233 252 272 40 h 108 156 204 181197 249 254 72 h 0 46 82 112 135 234 247 Relative extension [%] 72 h 017 29 42 50 88 85*)Comparison example

Example 8

Study of Separators with 1-Dodecanol in the Battery Test

Analogously to Examples 2 to 7 separators were coated with 3.5 wt.-%with 1-dodecanol. The weight ratio of filler to polymer was 2.2, the oilcontent 12 wt.-% Untreated separators served as comparison. Theseparators were tested in a lead/sulphuric acid battery. To this endbattery cells were assembled from antimony-containing positive platesand negative lead-calcium plates (five positive and four negative platesper cell) with a total capacity of 36 Ah/cell. Three cells were equippedwith the dodecanol-coated separators, the other three cells with theuntreated separators. The battery was subjected to an intensifiedstability test at 50° C. according to DIN 43539 Part 2 draft 10/1980.Then the cells were opened and the expansion of the separators in thepocket area and in the fold edge was determined.

The results of the battery test are compiled in Table 2. These showthat, even under conditions reflecting those encountered in practice,the additive used offers a noticeable improvement in protection of theseparator from oxidative attacks. TABLE 2 Oxidation resistance ofseparators after treatment with 1-dodecanol (battery test) Separatorwithout Separator with 3.5 additive*) wt.- % 1-dodecanol before testafter test before test after test Measuring point Absolute extension[%]**) in the pocket 493 ± 42 357 ± 46 513 ± 39 551 ± 49 area in thefold 493 ± 42 316 ± 24 513 ± 39 429 ± 33 edge Relative CMD expansion**)in the pocket 100% 72% 100% 107% area in the fold 100% 64% 100%  84%edge*)Comparison**)measured after 264 test cycles

Examples 9-11

Use of Fatty Alcohols as Additives to Prevent Premature Oxidation ofBattery Separators

Analogously to Examples 1 to 7 separators with alcoholic solutions of1-tetradecanol, 1-hexadecanol, and 1-octadecanol were coated on oneside. After drying there was in each case a quantity of 3.5 wt.-% of theadditive on the separator. The separators were subjected to theoxidation test described in Examples 1 to 7. The results are compiled inTable 3.

Separators which are coated with higher-molecular-weight fatty alcoholsalso show a clearly improved oxidation stability compared with theuntreated separator (Example 1). TABLE 3 Oxidation resistance ofseparators after treatment with fatty alcohols (oxidation test) Example6 9 10 11 Additive 1- 1- 1-hexadecanol 1-octadecanol dodecanoltetradecanol Quantity of 3.5 3.5 3.5 3.5 additive [wt.- %] Duration ofthe oxidation test Absolute extension [%]  0 h 267 271 271 268 20 h 252265 274 265 40 h 249 238 240 238 72 h 234 212 218 201 Relative extension[%] 72 h 88 78 80 75

Examples 12-14

Comparison of the Antioxidative Effect of Process Oil and Dodecanol

It is known from the state of the art that the oxidation resistance ofseparators can be improved by increasing the level of process oil. In acomparative, test the effect of the oil content on the oxidationstability was compared with the effect of the same quantity of anadditive according to the invention (1-dodecanol). The results are shownin Table 4. It is to be noted that the additive according to theinvention produces a much more noticeable improvement in oxidationresistance. The separators were produced and the test carried out asdescribed in Examples 1 to 7. The weight ratio of filler to polymer was2.4. In each case the oil was extracted to the content given in theTable. TABLE 4 Oxidation resistance of separators after treatment with1-dodecanol and raising of the oil content (oxidation test) Example 12*)13*) 14 Additive none none 1-dodecanol (3.5 wt.- %) Oil content 12.415.4 11.2 [wt.- %] Duration of oxidation test Absolute extension [%]  0h 407 431 419 20 h 313 370 406 40 h 218 346 388 72 h 99 204 326 96 h 077 218 Relative extension [%] 96 h 0 18 52*)Comparison example

Examples 15-18

Use of Alkoxylated Alcohols as Additives to Prevent Premature Oxidationof Battery Separators

Analogously to examples 1 to 7 separators were treated with alkoxylatedalcohols and then subjected to the oxidation test. The weight ratio offiller to polymer was. 2.6. Compounds of the general formulaR²—(OC₂H₄)_(p)—OH were studied, R² and p having the meaning given inTable 5. The results compiled in Table 5 show that the addition productsof ethylene oxide on long-chain alcohols can noticeably improve theoxidation resistance of battery separators. TABLE 5 Oxidation resistanceof separators after treatment with fatty alcohol ethoxylates (oxidationtest) Example 1*) 6 15 16 17 18 Additive: R²—(OC₂H₄)_(p)—OH R² C₁₂ C₁₂C₁₂ C_(16/18) C_(16/18) C_(16/18) P — — 2 2 5 11 Quantity of additive 03.5 3.5 3.5 3.5 3.5 [wt.- %] Duration of oxidation test Absoluteexpansion [%]  0 h 263 267 281 292 279 284 20 h 152 252 246 242 279 25740 h 108 249 224 260 227 234 72 h 0 234 145 212 159 84 Relativeexpansion [%] 72 h 0 88 52 73 57 30*)Comparison example

Example 19

Use of Phthalic Acid Esters as Additives to Prevent Premature Oxidationof Battery Separators

Analogously to Examples 1 to 7 separators were prepared and their oilcontent was set at 12 wt.-% by extraction with hexane. The weight ratioof filler to polymer was 2.2. Differently from Examples 1 to 7, 1 or 2wt.-% stearyl phthalate was added to the hexane bath for the treatmentof the separators according to the invention. The separators wereremoved from the bath following the extraction and dried at roomtemperature after dripping. After drying the separators contained 1 or 2wt.-% stearyl phthalate. According to Table 6 an effective protection ofthe separator against premature oxidation is achieved by stearylphthalate. Stearyl phthalate is split by the battery acid into phthalic,acid and octadeanol, an additive suitable according to the invention.TABLE 6 Oxidation resistance of separators after treatment with stearylphthalate (oxidation test) Additive none Stearyl phthalate 1 wt.- % 2wt.- % Duration of oxidation test Absolute extension [%]  0 h 498 498512 72 h 78 211 251 Relative extension [%] 72 h 16 42 49

Examples 20-26

Use of Polyacrylates as Additives to Prevent Premature Oxidation ofBattery Separators

Analogously to Examples 1 to 7 battery separators with a weight ratio offiller to polymer of 2.2 were prepared based on polyethylene (UHMWPE)and amorphous silicon dioxide. Differently from Examples 1 to 7,polyacrylic acid or the sodium salt of polyacrylic acid were added tothe separator material before extrusion, the quantities of polyacrylicacid present in the separator after extraction being given in Table 7.The separators were then subjected to the oxidation test. The resultscompiled in Table 7 show that salts of polyacrylic acid give aneffective protection of the separators against premature oxidationpossible. In contrast to this free to polyacrylic acid was practicallywithout effect. The results also show that polyacrylic acids are notwashed out of the separator during extraction. TABLE 7 Oxidationresistance of separators with polyacrylic acid (oxidation test) Example20*) 21 22 23 24 25 26*) Additive none Polyacrylic acid Averagemolecular — 1,200 4,000 8,000 15,000 30,000 100,000 weight [g/mol] Form— salt**) salt**) salt**) salt**) salt**) acid K-value***) — 15 25 30 4050 80 Concentration — 2.0 2.0 2.0 2.0 2.0 2.0 [wt.- %] Duration ofoxidation test Absolute extension [%]  0 h 508 522 468 530 499 504 44720 h 420 446 413 410 456 485 418 40 h 303 427 394 413 450 457 211 72 h21 333 273 240 244 224 16 Relative extension [%] 72 h 4 64 58 45 49 44 4*)Comparison example**)The sodium salt of polyacrylic acid was used (completely neutralizedform)***)Fikentscher's constant, measured in a 1-% aqueous solutionneutralized with sodium hydroxide solution, parameter forcharacterization of the degree of polymerization and the molar mass

Examples 27-28

Use of Polyacrylic Acid Copolymers as Additives to Prevent PrematureOxidation of Battery Separators

Analogously to Examples 20 to 26 separators were prepared and testedwhich contained polyacrylic acid copolymers instead of polyacrylic acid.In Example 27 the polymer Sokolan CP 10 was used, in Example 28 SokolanCP 10 S (both Fa. BASF, Ludwigshafen). The results are shown in Table 8.Here also the salt form of the polymers produces a good oxidationprotection while the acid form is, practically without effect. TABLE 8Oxidation resistance of separators with polyacrylic acid copolymers(oxidation test) Example 23*) 27 28 Additive none Polyacrylic acidcopolymer Average molecular — 4,000 4,000 weight [g/mol] Form — salt**)acid Concentration [wt.- %] — 2.0 2.0 Duration of Absolute oxidationtest extension [%]  0 h 508 521 556 20 h 420 465 506 40 h 303 433 375 72h 21 279 43 Relative extension [%] 72 h 4 54 8*)Comparison example**)The sodium salt of polyacrylic acid was used (completely neutralizedform)

1. Battery separator based on thermoplastic, ultra-high molecular-weightpolyolefin with an average molecular weight by weight of at least300,000, comprising, relative to the sum of the weights of filler andpolyolefin, 10 to 100 wt.-% polyolefin and 0 to 90 wt.-% filler, and,relative to the weight of the separator, 5 to 35 wt.-% oil and 0.5 to5.0 wt.-% of a compound according to the Formula (I)R(OR¹)_(n)(COOM^(X+) _(1/x))_(m)  (I) in which R is a non-aromatichydrocarbon radical with 10 to 4200 hydrocarbon atoms, which can beinterrupted by oxygen atoms, R¹ is H, —(CH₂)_(k)COOM^(X+) _(1/x) or—(CH₂)_(k)—SO₃M^(X+) _(1/x), where k is 1 or 2, M is an alkali metal oralkaline-earth metal ion, H⁺ or NH₄ ⁺, where not all the M variablessimultaneously have the meaning H⁺, n is 0 or 1, m is 0 or an integerfrom 10 to 1400 and x is 1 or 2, the ratio of oxygen atoms to carbonatoms in the compound according to Formula (I) lying in the rangebetween 1:1.5 to 1:30 and m and n not being able to simultaneously be 0.2. Battery separator according to claim 1, wherein R is a hydrocarbonradical with 10 to 180 carbon atoms, which can be interrupted by 1 to 60oxygen atoms, n is 1, m is 0 and x is 1 or
 2. 3. Battery separatoraccording to claim 2, wherein R is a hydrocarbon radical of the formulaR²—[(OC₂H₄)_(p) (OC₃H₆)_(q)]—, in which R² is an alkyl radical with 10to 30 carbon atoms, p is an integer from 0 to 30 and/or q is an integerfrom 0 to
 30. 4. Battery separator according to claim 3, wherein p is aninteger from 0 to 10 and q is an integer from 0 to
 10. 5. Batteryseparator according to claim 3, wherein the sum of p and q is smallerthan or equal to
 10. 6. Battery separator according to claim 2, whereinR¹ is H.
 7. Battery separator according to claim 1, wherein R is analkane radical with 20 to 4200 carbon atoms, M is an alkali metal oralkaline-earth metal ion, H⁺ or NH₄ ⁺, where not all the variables Msimultaneously have the meaning H⁺, n is 0, m is an integer from 10 to1400 and x is 1 or
 2. 8. Battery separator according to claim 7, whereinR is an alkane radical with 50 to 750 carbon atoms.
 9. Battery separatoraccording to claim 7, wherein the compound according to Formula (I) is apoly(meth)acrylic acid, whose acid groups are at least partlyneutralized.
 10. Battery separator according to claim 9, wherein atleast 40% of the acid groups of the poly(meth)acrylic acid areneutralized.
 11. Battery separator according to claim 7, wherein M isLi⁺, Na⁺ or K⁺.
 12. Battery separator according to claim 7, wherein thepoly(meth)acrylic acid has an average molar mass M_(w) of 1,000 to100,000 g/mol.
 13. Battery separator based on thermoplastic, ultra-highmolecular-weight polyolefin with an average molecular weight by weightof at least 300,000, comprising a component which, when the separator isused for the intended purpose, can form a compound of the Formula (I):R(OR¹)_(n)(COOM^(X+) _(1/x))_(m)  (I) in which R is a non-aromatichydrocarbon radical with 10 to 4200 hydrocarbon atoms, which can beinterrupted by oxygen atoms, R¹ is H, —(CH₂)_(k)COOM^(X+) _(1/x) or—(CH₂)_(k)—SO₃M^(X+) _(1/x), k being 1 or 2, M is an alkali metal oralkaline-earth metal ion, H⁺ or NH₄ ⁺, where not all the M variablessimultaneously have the meaning H⁺, n is 0 or 1, m is 0 or an integerfrom 10 to 1400 and x is 1 or 2, the ratio of oxygen atoms to carbonatoms in the compound according to Formula (I) lying in the rangebetween 1:1.5 to 1:30 and m and n not being able to simultaneously be 0.14. Lead-sulphuric acid accumulator with at least two oppositely-chargedelectrode plates, comprising at least one battery separator according toclaim
 1. 15. Process for the preparation of a battery separatoraccording to claim 1, wherein a compound with the Formula (I) or asolution of a compound with the Formula (I) is applied to a batteryseparator and the separator is then optionally dried.
 16. Process forthe preparation of a battery separator according to claim 1, wherein ahomogenous mixture of ultra-high molecular-weight thermoplasticpolyolefin, at least one compound with the Formula (I) and optionallyfiller and further additives are prepared, formed into a web-shapedmaterial and then one or more of the further additives are optionallyremoved.
 17. Method for the preparation of battery separators comprisingthe addition of a compound with the Formula (I) to a separator. 18.Method for the improvement of the oxidation resistance of batteryseparators comprising the addition of a compound with the Formula (I) toa separator.
 19. Battery separator according to claim 4, wherein the sumof p and q is smaller than or equal to
 10. 20. Battery separatoraccording to claim 8, wherein the compound according to Formula (I) is apoly(meth)acrylic acid, whose acid groups are at least partlyneutralized.
 21. Battery separator according to claim 20, wherein atleast 40% of the acid groups of the poly(meth)acrylic acid areneutralized.